RE: [PATCH v2 1/6] x86/bugs: Add asm helpers for executing VERW

[H. Peter Anvin]

On October 24, 2023 11:49:07 AM PDT, "Luck, Tony" <tony.luck@xxxxxxxxx> wrote:
>> the only overhead to modules other than load time (including the runtime linking) is that modules can't realistically be mapped using large page entries.
>
>If there were some significant win for using large pages, couldn't the
>kernel pre-allocate some 2MB pages in the [-2GiB,0) range?  Boot parameter
>for how many (perhaps two for separate code/data pages). First few loaded
>modules get to use that space until it is all gone.
>
>It would all be quite messy if those modules were later unloaded/reloaded
>... so there would have to be some compelling benchmarks to justify
>the complexity.
>
>That's probably why Peter said "can't realistically".
>
>-Tony
>

Sure it could, but it would mean the kernel is sitting on an average of 6 MB of unusable memory. It would also mean that unloaded modules would create holes in that memory which would have to be managed.